It has long been known that worn tires can be reconditioned by applying new tread stock to a prepared tire carcass and a whole retreading industry has been built up about this concept. In the past the new tread stock was applied to the carcass in an unvulcanized condition, the prepared tire was then put into a mold, the tire pressurized from within, and the mold was then heated to vulcanize the tread. The process was time-consuming because of the necessity of bringing the entire tire and tread to curing temperature from the mold surface inwardly, and costly because the retreading molds were expensive.
It has more recently been proposed to apply the new tread as a precured band or strip. In this method it is only necessary to cure a thin layer of cushion gum stock between the tread and prepared carcass. This can be done in a simple pressurized chamber instead of the expensive molds previously required. It has been found, however, that difficulties are encountered in achieving proper adherence between the circumferential edges of the new tread and the carcass. In applying the tread strip or band, the carcass is distorted to reduce the circumference by spreading the beads of the tire carcass apart and the tread stock is then applied and "stitched" or rolled in place to promote adhesion between the carcass and an applied cement and cushion gum layer and to eliminate, so far as possible, any air bubbles which would later on cause a failure of the bond between the applied tread and the carcass. Failure of the bond, of course, leads to throwing the tread from the tire during running, and usually at high speeds and high load.
It has been found that failure of the adhesion between the tread stock and tire carcass starts at the circumferential edges and results from the tread being insufficiently pressed against the carcass in the edge area during the curing step.
The present invention overcomes the problems previously presented to the art by continuously applying, during curing, a very high pressure to the edge area of the precured tread stock. In the invention, the tread stock is provided with a circumferential series of holding lugs which form grooves on each side of the tread. Hoops or rings having a fixed circumference are placed in the grooves while the tire carcass is on the conventional spreader and when released from the spreader, the hoops serve to draw the tread stock down over the tire carcass with a high pressure on the tread and carcass which is retained during curing. After curing, the holding lugs are cut off and the hoops removed and reused.